In institutional and industrial washing processes the wastewater of the washing process is usually cleaned and purified by using membrane filtration units. The obtained purified water can then be re-used in another washing cycle. The use of a membrane filtration process for the cleaning of wastewater results in a decrease of the amount of fresh water required to be added to the washing cycle and accordingly in a reduction of costs and saving resources. Also from an environmental point of view the use of membrane filtration is advisable.
However, the membrane cleaning processes can only be applied for wastewater which does not contain components blocking the membrane of the membrane filtration unit. Therefore it is necessary to use membrane-compatible detergents in these washing processes which do not contain any membrane-blocking or membrane-destroying components.
In the state of the art membrane-compatible detergent compositions are already known. However, most of these detergents are detergents in paste form having a high viscosity that changes significantly with temperature and strongly increases at low temperatures.
WO 02/46351 A1 describes for example a membrane-compatible paste-like composition which is used in a washing process in which the wastewater is purified by a membrane filtration unit and especially in a membrane filtration unit comprising one or more reverse osmosis steps. The detergent comprises non-ionic surfactants, an alkalinity source, and water.
As non-ionic surfactants linear fatty alcohol alkoxylates are used which are ethoxylated. Furthermore the composition comprises alkyl polyglycoside having 8 to 14 carbon atoms.
The paste has a high viscosity being between 50,000 to 250,000 mPas at 5 and/or 50 revolutions per minute measured using a Brookfield rotational viscosimeter with spindle no. 7 at 25° C.
A further pasty soap detergent is described in WO 2005/118760 A1. This detergent is also used in a washing process in which the accumulated wastewater is cleaned by a filtration process using a membrane filtration unit. The detergent comprises anionic surfactants, non-ionic surfactants, an alkalinity source, and an organic and/or inorganic builder on a non-silicate basis. Furthermore the composition is free of greying inhibitors on a cellulose basis, silicates, and phosphates.
As non-ionic surfactants linear fatty alcohol alkoxylates are used which are ethoxylated. Furthermore the composition comprises alkyl polyglycoside having 8 to 14 carbon atoms.
The paste has a an even higher viscosity being between 50,000 to 300,000 mPas at 5 and/or 50 revolutions per minute measured using a Brookfield rotational viscosimeter with spindle no. 7 at 25° C.
Liquid detergents are also known from the state of the art. Such detergents are, for example, described in U.S. Pat. No. 5,880,083, WO 2004/065535 A1, and WO 2004/041990 A1. However, the liquid detergents being used in the state of the art often contain components causing the blocking of the membrane filtration unit and hence cannot be used for washing processes in which membrane filtration units are used for the cleaning of the wastewater. Those components, if used in high amounts, are for instance cationic surfactants, certain emulsifiers, carboxymethylcellulose and silicates. These components immediately block the membrane and lead to an interruption of the whole washing process. By leaving out such components the stability of the liquid detergent composition which normally is an emulsion or dispersion decreases. This decreased stability results in a separation of the emulsion or the dispersion after storage or when used at extremely different temperatures. Separated emulsions or dispersions cannot be used in the washing process and cannot be dosed applying the usual dosing units.